The approach and landing is the most difficult phase of a flight due to the precision actions required and increased pilot workload. While flying the instrument approach, pilots are trained to monitor progress and make adjustment with reference to the flight instruments, e.g., the Flight Director (FD), the glide path deviation scale, and the Horizontal Situation Indicator (HSI). These standard flight instruments which are driven by a Flight Management System (FMS) have been designed to provide guidance cues in an accurate and unambiguous manner. Governmental bodies throughout the world, such as the Federal Aviation Administration (FAA) in the United States, provide standards and certify FMS software for general safety in the aviation industry. The certification of the FMSs are rated at a specific Design Assurance Level (DAL), which is determined from the safety assessment process and hazard analysis by examining the effects of a failure condition in the system.
Many aircraft FMSs are designed and certified to software DAL C (level C), as defined in DO-178B, Software Considerations in Airborne Systems and Equipment Certification. However, many instrument approaches require a navigation system certified to DAL B. Therefore, a level C FMS is not able to fly these more stringent approaches.
RNP is RNAV with the addition of an onboard performance monitoring and alerting capability. A defining characteristic of RNP operations is the ability of the aircraft navigation system to monitor the navigation performance it achieves and inform the crew if the requirement is not met during an operation. This onboard monitoring and alerting capability enhances the pilot's situation awareness and can enable reduced obstacle clearance or closer route spacing without intervention by air traffic control.
RNP is a type of performance-based navigation that defines the level of performance required by an aircraft for a specific maneuver, for example, the approach to an airport. The current specific requirements of an RNP system include the capability to follow a desired ground track, including curved paths, with reliability, repeatability and predictability; and where vertical profiles are included for vertical guidance, use of vertical angles or specific altitude constraints are used to define a desired vertical path. Performance monitoring and alerting capabilities may be provided in different forms depending on the system installation, architecture and configurations, including display and indication of both the required and the estimated navigation system performance; monitoring of the system performance and alerting the crew when RNP requirements are not met; and cross track deviation displays scaled to RNP, in conjunction with separate monitoring and alerting for navigation integrity.
An RNP system utilizes its navigation sensors, system architecture, and modes of operation to satisfy the RNP navigation specification requirements. It must perform the integrity and reasonableness checks of the sensors and data, and may provide a means to deselect specific types of navigation aids to prevent reversion to an inadequate sensor. RNP requirements may limit the modes of operation of the aircraft where flight technical error (FTE) is a significant factor. Dual system/sensor installations may also be required depending on the intended operation or need.
Generally, aircraft utility is increased through the capability to fly to lower minimums, or a minimum altitude below which the crew either sees the runway or executes a missed approach. In RNP approaches, the lower the minimums, the lower the RNP value. Current certification guidance allows an RNP value of 0.3 NM (the width of the path in which the airplane is expected to remain) to be flown by an FMS with DAL C. For lower values of RNP, for example, 0.29 NM down to 0.10 NM, which translate to lower minimums, current certification guidance expects the FMS (and other critical avionics) to be certified to DAL B.
Accordingly, it is desirable to provide a system and method for improving the ability of an aircraft to navigate by improving navigation reliability. Furthermore, other desirable features and characteristics of the exemplary embodiments will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.